544 BACTERIOLOGY. 



the course of infection by the organisms themselves. 

 Also, that by the systematic injection of susceptible ani- 

 mals with sublethal doses of such poisons it is possible 

 to endow the animal with a degree of tolerance to that 

 poison. When in this state the blood of that animal 

 contains a specific antidote for the poison, though it may 

 have no effect upon the bacteria by which it was pro- 

 duced. This antidotal relationship may be demonstrated 

 in a test tube by mixing the poison with the blood serum 

 of the animal. In some instances these poisons toxins, 1 

 as they are collectively called appear to be the direct 

 result of metabolic changes brought about by bacteria in 

 the medium or tissues in which they may be developing 

 i. e.j they are by-products of nutrition that pass read- 

 ily into solution, as is conspicuously seen in the case of 

 the bacillus of diphtheria and of tetanus when under 

 both artificial cultivation and in the animal body. On 

 the other hand, certain bacteria do not possess the power 

 of generating or secreting such poisons ; they have, never- 

 theless, intimately associated with their protoplasmic 

 bodies poisonous substances ("endotoxins") that mani- 

 fest themselves only when these organisms gain access to 

 living susceptible tissues ; thus the toxins of bacterium 

 tuberculosis and of microspira comma are much more 

 conspicuously present in the protoplasm of these bacteria 

 than in the fluids in which they have grown. 



Buchner has isolated from several species of bacteria 

 u bacterioproteins " having the common properties of 



i The term " toxins " is commonly applied to amorphous, nitrogenous 

 poisons produced by bacteria in both living tissues and dead sub- 

 stances; while, on tne other hand, the term "ptomains" relates to 

 crystallizable, nitrogenous poisons that are formed in dead tissue, and 

 "leucomains" to poisonous and non-poisonous alkaloidal bodies that 

 occur in living tissues as a result of physiological metabolism, 



